System and method for selective registration in a multi-beam system

ABSTRACT

A system and method for selective registration of a user equipment (UE) to one of a plurality of access points (APs). An indication may be received that each of a plurality of APs have received a signal from a UE. The UE may be registered to the first one of the plurality of APs to satisfy registration requirements associated with the UE. Information may be reported to a controller related to the signal strength of communication received at each AP from the UE. If the signal strength received at the registered AP is less than the signal strength received at one or more of the non-registered APs by more than a threshold amount, the registration of the UE to the registered AP may be rejected.

FIELD OF THE INVENTION

The present invention relates generally to the field of radio frequency(RF) multiple-input-multiple-output (MIMO) systems and in particular tosystems and methods for enhanced performance of RF MIMO systems using RFbeamforming and/or digital signal processing (DSP). Embodiments of thepresent invention relate to the following fields and technologies: WiFi,Institute of Electrical and Electronics Engineers (IEEE) 802.11a, b, g,n, ac standards, antenna arrays, side lobe reduction, receivers,transmitters, beamforming, DSP, digital filtering, analog and digitalsignal cancellation and interference mitigation.

BACKGROUND OF THE INVENTION

Prior to setting forth a short discussion of the related art, it may behelpful to set forth definitions of certain terms that will be usedhereinafter.

The term “MIMO” as used herein, is defined as the use of multipleantennas at both the transmitter and receiver to improve communicationperformance. MIMO offers significant increases in data throughput andlink range without additional bandwidth or increased transmit power. Itachieves this goal by spreading the transmit power over the antennas toachieve spatial multiplexing that improves the spectral efficiency (morebits per second per Hz of bandwidth) or to achieve a diversity gain thatimproves the link reliability (reduced fading), or increased antennadirectivity.

The term “beamforming” sometimes referred to as “spatial filtering” asused herein, is a signal processing technique used in antenna arrays fordirectional signal transmission or reception. This is achieved bycombining elements in the array in such a way that signals at particularangles experience constructive interference while others experiencedestructive interference. Beamforming can be used at both thetransmitting and receiving ends in order to achieve spatial selectivity.

The term “beamformer” as used herein refers to RF and/or digitalcircuitry that implements beamforming and includes combiners and phaseshifters or delays and in some cases amplifiers and/or attenuators toadjust the weights of signals to or from each antenna in an antennaarray. Digital beamformers may be implemented in digital circuitry suchas a digital signal processor (DSP), field-programmable gate array(FPGA), microprocessor or the CPU of a computer to set the weights(phases and amplitudes) of the above signals. Various techniques areused to implement beamforming such as using a Butler matrix, BlassMatrix, Rotman Lens and/or phased array of antennas. In general, mostapproaches to beamforming attempt to provide simultaneous coveragewithin a sector using multiple beams.

WiFi has been implemented with a limited amount of frequency resourcesthat use techniques of collision avoidance to allow multiple userequipment (UEs) to share the same channel. As the numbers of UEsproliferate, the impact of such a scheme restricts the ability of a basestation Access Point (AP) to support many users without impacting theperformance to and from each. This invention discloses an apparatus andmethods to allow the reuse of resources by implementing AP clustersusing multi-beam antennas breaking down a sector area of coverage intosmaller subsectors. In order to accomplish this, several limitations ofmulti-beam antennas must be addressed. First, since WiFi is a timedivision multiplex system (TDD), the transmitting and receivingfunctions use the same channel. Unsynchronized operation between APsmeans a transmitting AP's signal may interfere with the reception ofanother AP that uses the same channel unless sufficient isolation (e.g.,125 dB) is provided between the transmitting and receiving functions.Prior art cited above addresses the problem by using physicallyseparated antenna arrays for transmit and receive and by providingcancellation of each transmitted signal within the receiver processingfunctions. Another limitation is that multi-beam antennas do not offerinfinite separation of the coverage of one beam to the others. Thefollowing discusses the impacts of this performance limitation andpresents approaches to mitigate its effect.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Beamforming networks include multi-beam antenna arrays to providemultiple beams pointed at different directions to independentlycommunicate with multiple respective APs. In order to provide continuouscoverage to UEs throughout a sector, the coverage of adjacent beams of amulti-beam antenna overlap. This presents a potential for interferencewhen adjacent beams illuminate the same area on the same frequencies orchannel. In order to reduce such interference from one beam to another,adjacent beams may provide communication over different channels.

To register to an AP, UEs typically scan channels for an available APand stop searching upon finding a first AP that satisfies theirregistration requirements. However, when a communication link issufficiently strong, APs and/or frequencies outside of the UE's optimalrange may provide sufficiently strong signals to satisfy the UE'sregistration requirements, causing the UE to register to a sub-optimalAP. Further, as a UE moves from one beam to the next, commonly referredto as “roaming,” an AP and/or frequency that is optimal in one locationbecomes sub-optimal as the UE travels to another location. The problemof roaming may be compounded for UEs that are close to APs since theytravel across beams more quickly and, because of their proximity to theantennas, experience relatively good communication causing registrationto the “wrong” AP to be more likely.

According to an embodiment of the invention, a system and method isprovided for detecting registration to sub-optimal APs and/orfrequencies and providing means to re-register the UE to an optimal APand/or frequency.

According to an embodiment of the invention, a system and method isprovided for selective registration of a user equipment (UE) to one of aplurality of access points (APs) in a multi-beam system. An indicationmay be received that each of a plurality of APs have received a signalfrom a single UE. The UE may communicate with each AP over an associatedbeam that includes a primary lobe providing a relatively higher signalstrength surrounded by one or more sidelobes providing a relativelylower signal strength. The UE may register to a first one of theplurality of APs that satisfies registration requirements associatedwith the UE. The registration of the UE to the registered AP may bemaintained if the UE communicates with the registered AP over a primarylobe providing a greater than threshold relative signal strengthrelative to the other (non-registered) APs, whereas the registration ofthe UE to the registered AP may be rejected when the UE communicateswith the registered AP over a sidelobe or over a primary lobe providinga less than threshold relative signal strength relative to the otherAPs.

According to an embodiment of the invention, a system and method isprovided for selective registration of a UE to one of a plurality ofaccess points (APs). An indication may be received that each of aplurality of APs have received a signal from a user equipment (UE). TheUE may be registered to the first one of the plurality of APs to satisfyregistration requirements associated with the UE. Information may bereported to a controller related to the signal strength of communicationreceived at each AP from the UE. If the signal strength received at theregistered AP is less than the signal strength received at one or moreof the non-registered APs by more than a threshold amount, theregistration of the UE to the registered AP may be rejected.

Another problem in multi-beam systems is sidelobe interference caused bynon-ideal directivity of the beams. A beam may include a primary lobe(PL) pointed along a main axis or direction of the beam and whichtypically provides relatively high signal gain, amplitude or power. Theprimary lobe may be surrounded by a sidelobe (SL), which may be an echoof the primary lobe, and which typically provides relatively lowersignal gain, amplitude or power. Sidelobes (SL) radiate in directionsaskew from the main direction or axis of the beam and thus, aretypically a source of interference when transmitting in those othersidelobe directions. Sidelobes may simultaneously receive energy, notonly from UEs along the beam path, but also from UEs that are notlocated within the beam path.

Various techniques may be used to reduce, suppress or cancel sidelobesignals. One sidelobe suppression technique is referred to as “tapering”or “Taylor weighting,” in which the gain or amplitude of each antennaelement may be weighted differently depending on its position in theantenna array. Typically the gain or amplitude of an antennae element isweighted lower the farther the antenna is positioned from the center ofthe antenna array. However, to achieve acceptable performance, taperingtypically requires antenna arrays with a substantially large number ofantenna elements (e.g. greater than eight).

According to an embodiment of the invention, a system and method isprovided for sidelobe suppression with any number (e.g. four) antennaelements.

According to an embodiment of the invention, a system and method isprovided for selective suppression of sidelobe signals using controlledsignal cancellation. An indication may be received that a signal from asingle user equipment (UE) is received at each of two or more accesspoints (APs) over the same channel. The relatively stronger power signalmay be received over a primary lobe of a communication beam of one ofthe APs and the relatively weaker power signal may be received over aside lobe of a communication beam of another one of the APs. Theefficacy of signal cancellation may be tested by turning signalcancellation on and off to measure the UE signals received at one of theAPs. If interference is lower when signal cancellation is turned on,said signal cancellation may be applied for continued communication withsaid UE to cancel side lobe signals and if interference is lower whensignal cancellation is turned off, said UE may be communicated withwithout applying said signal cancellation.

According to an embodiment of the invention, a system and method isprovided for selective suppression of sidelobe signals using controlledsignal cancellation. Signals may be transmitted/received to/from aplurality of access points (APs) along the direction of a plurality of(N) different respective beams, wherein each of the plurality of (N)beams includes a primary lobe providing relatively high signal powersurrounded by two or more side lobes providing relatively low signalpower, wherein a primary lobe of one beam is substantially separatedfrom a primary lobe of an adjacent beam communicating over the samechannel but at least partially overlapping one or more side lobes of theadjacent beam. It may be determined if user equipment (UE) detected bytwo or more APs is communicating using a side lobe signal or a primarylobe signal. Signal cancellation may be applied to suppress the sidelobesignals if the UE is determined to communicate using a sidelobe signalbut not applied if the UE is determined to communicate using a primarylobe signal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention and in order to show how itmay be implemented, references are made, purely by way of example, tothe accompanying drawings in which like numerals designate correspondingelements or sections. In the accompanying drawings:

FIG. 1 is a schematic illustration of a multi-beam system including aplurality of access points driving one or more beamformers and anantenna array to create a plurality of beams in accordance with anembodiment of the invention;

FIG. 2 is a schematic illustration of a sector coverage area subdividedinto subsector zones covered by multiple beams in accordance with anembodiment of the invention;

FIG. 3 is a schematic illustration of a multi-beam system using digitalbeamformers in accordance with an embodiment of the invention;

FIG. 4 is a schematic illustration of a multi-beam system with separatedtransmit and receive circuitry in accordance with an embodiment of theinvention;

FIG. 5 is a schematic illustration of a radiation pattern of amulti-beam system in accordance with an embodiment of the invention;

FIG. 6 is a schematic illustration of a radiation pattern of amulti-beam system as shown in FIG. 5 that is tapered in accordance withan embodiment of the invention;

FIG. 7 is a schematic illustration of a multi-beam system for optimallyregistering UEs to APs in accordance with an embodiment of theinvention;

FIG. 8 is a schematic illustration of a radiation pattern for theantenna array of FIG. 7 in accordance with an embodiment of theinvention;

FIG. 9 is a schematic illustration of a multi-beam system for taperingand signal cancellation in accordance with an embodiment of theinvention;

FIG. 10 is a schematic illustration of a radiation pattern transmittedby the antenna array of FIG. 9 with and without signal cancellation inaccordance with an embodiment of the invention;

FIG. 11 is a schematic illustration of a radiation pattern transmittedby the antenna array of FIG. 9 with tapering and selective signalcancellation in accordance with an embodiment of the invention;

FIG. 12 is a schematic illustration of a multi-beam system for selectivesignal cancellation using digital beamforming in accordance with anembodiment of the invention;

FIG. 13 is a schematic illustration of a multi-beam system for selectivesignal cancellation using digital beamforming in accordance with anembodiment of the invention; and

FIGS. 14-15 are flowcharts of methods in accordance with embodiments ofthe invention.

The drawings together with the following detailed description make theembodiments of the invention apparent to those skilled in the art.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

It is stressed that the particulars shown are for the purpose of exampleand solely for discussing the preferred embodiments of the presentinvention, and are presented in the cause of providing what is believedto be the most useful and readily understood description of theprinciples and conceptual aspects of the invention. In this regard, noattempt is made to show structural details of the invention in moredetail than is necessary for a fundamental understanding of theinvention. The description taken with the drawings makes apparent tothose skilled in the art how the several forms of the invention may beembodied in practice.

Before explaining the embodiments of the invention in detail, it is tobe understood that the invention is not limited in its application tothe details of construction and the arrangement of the components setforth in the following descriptions or illustrated in the drawings. Theinvention is applicable to other embodiments and may be practiced orcarried out in various ways. For example, although the following figuresdescribe four or eight beam systems, any number of a plurality of beamsmay be used greater than or equal to two. Also, it is to be understoodthat the phraseology and terminology employed herein is for the purposeof description and should not be regarded as limiting.

Reference is made to FIG. 1, which schematically illustrates amulti-beam system 100 including a plurality of access points 101 drivingone or more beamformers 103 and an antenna array 102 to create aplurality of beams 104 in accordance with an embodiment of theinvention. Each of the plurality of beams 104 may be pointed towarddifferent directions to spatially divide communication into multipletransmission zones using phased array technology. The zones may bedivided in one-dimension (along the azimuth direction only) or intwo-dimensions (along the azimuth and zenith/elevation directions). Eachaccess point 101 may independently control a single corresponding beam104 to simultaneously communicate independently with the user equipmentin each zone using the same radio channel. Each zone may be occupied byzero, one or multiple mobile devices serviced by a single beam or datastream.

Reference is made to FIG. 2, which schematically illustrates a sectorcoverage area 225 subdivided into subsector zones covered by multiplebeams 221-224 in accordance with an embodiment of the invention. UEs211-216 located in the subsector zones may communicate with accesspoints 201-204 over beams 221-224. User devices may scan the channelsfor the first available access point that satisfies its registrationrequirements. User device 215 in the zone covered by beam 221 mayregister to access point 201, user devices 212 and 211 in the zonecovered by beam 222 may register to access point 202, user device 216 inthe zone covered by beam 223 may register to access point 203, and userdevice 214 in the zone covered by beam 224 may register to access point204. A user device 213 near zone boundaries may register to eitheraccess point 201 or 202. Although FIG. 2 shows an idealized partition ofarea 225 into subsector zones with adjacent beams having perfectlycoinciding and non-overlapping boundaries, adjacent beams may overlapcausing interference (e.g. see FIGS. 5 and 6).

Reference is made to FIG. 3, which schematically illustrates amulti-beam system 300 using digital beamformers 303 in accordance withan embodiment of the invention. To transmit signals over multiple beams304, a plurality of AP baseband stations 301 may provide basebandsignals to digital beamformers contained in logical block elements ofbeamformers 303. Beamformers 303 may output digitized intermediatefrequency (IF) signals that are converted to analog signals in radios305, upconverted, and then radiated by antennas 302 to create radiatedbeams 304. To receive signals over multiple beams 304, the process isreversed. Signals received over beams 304 by antennas 302 are amplified,downconverted and digitized in radios 305. The digitized IF signals maythen be processed by the beamformer logical block elements ofbeamformers 303 to isolate the individual received beam signals androute those signals to the appropriate AP baseband station 301.

In WiFi systems, an AP typically transmits and receives signals over thesame frequency at alternating times using a time division duplex (TDD)protocol. Ideally, each individual AP should not create interferencebetween transmitted and received signals because the AP will not betransmitting and receiving at the same time. However, in multi-beamsystems (e.g. system 100 of FIG. 1) using multiple APs (e.g. APs 101 ofFIG. 1), one AP may be transmitting at the same time as another AP isreceiving. Accordingly, transmitted signals from the one AP may becoupled to the receiving circuits of the other AP and createinterference at that AP. Such coupling may be due to insufficientisolation between transmit and receive circuits. One way to mitigate theproblem of coupling is to physically separate the transmit and receiveantenna arrays as shown in FIG. 4.

Reference is made to FIG. 4, which schematically illustrates amulti-beam system 400 with separated transmit and receive circuitry inaccordance with an embodiment of the invention. The transmit circuitrymay include a plurality of (N) APs 401 that generate transmit signals toa plurality of (N) transmit beamformers 405 which drive transmit antennaarray 406 including a plurality of (M) antennas to create a plurality of(N) transmit beams 407. The receive circuitry operates in reverse andincludes a receive antenna array 403 including a plurality of (M)antennas to receive a plurality of (N) of receive beams 404 and to beused in conjunction with a plurality of (N) receive beamformers 402 tocreate received signals for each individual AP 401. APs 401 may reportreceived signal parameters to a controller 408. Embodiments of theinvention may either be performed with analog beamformers or digitalbeamformers. In general, the number of beams (N) and APs (N) in each ofthe transmit or receive circuitry of system 400 is less than or equal tothe number of antennas (M) in each of the transmit or receive antennaarrays 403 or 406 (N≦M).

Reference is made to FIG. 5, which schematically illustrates a radiationpattern of a multi-beam system including a plurality of (e.g., N=8)beams 501 transmitted by an antenna array including a plurality of(e.g., N=8) antenna elements in accordance with an embodiment of theinvention. The antenna array may be coupled to a beamformer to generatethe signals using beamforming (e.g., Butler matrix) techniques. Each ofthe (N) beams 501 may include a primary lobe 503 having a relativelyhigher gain or amplitude and sidelobes 502 having a relatively lowergain or amplitude. Primary lobe 503 of each beam 501 may be oriented ina different direction along a main axis of symmetry of the beam 501(e.g. away from the emission plane of the antenna array) and sidelobes502 of each beam 501 may be oriented in directions askew or surroundingthe main axis of symmetry of the beam 501. To minimize interference, theratio of the gain/amplitude of primary lobes 503 to the gain/amplitudeof sidelobes 502 is preferably more than a threshold, for example,approximately 20 dB. In the example shown in FIG. 5, the ratio isapproximately 13 dB, which may be below the threshold. Accordingly, asidelobe suppression technique, such as, tapering or Taylor weighting,may be used to reduce the sidelobe interference of antenna arrays asshown in FIG. 6.

Reference is made to FIG. 6, which schematically illustrates a radiationpattern of a multi-beam system as shown in FIG. 5 that is tapered, forexample, using Taylor weighting, in accordance with an embodiment of theinvention. The antenna array generates a plurality of (e.g., N=8) beams,each beam including a primary lobe 601 and sidelobe 602. In the exampleshown in FIG. 6, the ratio of primary lobe 601 to sidelobe 602 may beincreased to approximately 30 dB. Although Taylor weighting may reducesidelobe interference, effective tapering typically requires asubstantially large antenna array. For example, an eight element linearantenna array is typically about 1.5 feet across for 2.4 GHz WiFi bandcoverage. This size may increase when using separate transmit/receivecircuits as shown in FIG. 4. For example, an array with 3 feet ofspacing between two 1.5 feet transmit/receive antenna arrays may resultin a 6 foot antenna structure. Devices may become even more cumbersomewhen using digital beamformers e.g. as shown in FIG. 3. For example, a(N=8) beam system may use 16 radios, which may add complexity tocalibrate those radios. Further, large tapered arrays may result inhighly overlapped coverage of adjacent beams.

Reference is made to FIG. 7, which schematically illustrates amulti-beam system 700 for optimally registering UEs to APs in accordancewith an embodiment of the invention. Multi-beam system 700 may include aplurality of access points 701 driving one or more beamformers 703 andan antenna array 702 to create a plurality of beams 704-707 controlledby controller 708. Beamformer 703 may be analog or digital. AlthoughFIG. 7 shows four access points 701, four antennas 702, and four beams704-707, any number of such components greater than four (or greaterthan two) may be used. When using separate transmit/receive circuits asshown in FIG. 4, the circuitry configuration shown in FIG. 7 may be usedfor each of the transmitter circuitry and the receiver circuitry.

Adjacent beams 704-707 may overlap in coverage causing one beam (e.g.beam 705) to interfere with communications on adjacent beams (e.g. beams704 and 706). To minimize interference near beam boundaries, adjacentbeams may communicate over different frequency channels. In FIG. 7,beams 704 and 706 may be operated on one channel (indicated in thefigure by shading) and beams 705 and 707 may be operated on a differentchannel (indicated in the figure by no shading) to provide frequencyisolation between coverage areas. Although alternating channels acrossadjacent beams reduces interference, other sources of interference, inparticular, sidelobe interference among the co-channel beams remains, asshown in FIG. 8.

Reference is made to FIG. 8, which schematically illustrates a radiationpattern for the antenna array of FIG. 7 in accordance with an embodimentof the invention. FIG. 8 shows the radiation gain/amplitude versus theazimuth of a signal transmitted by the antenna array of FIG. 7. In theexample of FIG. 8, the radiation pattern is generated using a Butlerbeamformer with four isotropic radiators, although any other beamformerand/or radiator may be used. A four antenna four beam system is shown inthe example of FIG. 8, although the figure and accompanying descriptionmay be generalized to a multi-beam system having any number of antennaelements and beams.

In FIG. 8, beams 801, 802, 803 and 804 are respectively identified asbeams 2L, 1L, 1R and 2R to designate their positions to the left andright relative to the direction normal to the emission plane of theantenna array. The subsector coverage areas of beams 801-804 (e.g. eachdefining a range of azimuth values relative to the antenna radiationplane) are identified by lines 805-809 (e.g. each defining a singleazimuth value) that represent the subsectors boundaries. Dashed line 812shows that the gain/amplitude of each primary lobe is approximately 13dB greater than the gains/amplitudes of sidelobes from other beams. Thegain of each beam's primary lobe at its boundary with adjacent primarylobes is approximately 4 dB lower than the beam's maximum gain trace.Accordingly, the worst case of interference caused by a sidelobe mayprovide a gain ratio of approximately 9 dB in the example of FIG. 8.Since a UE typically scans multiple channels and registers with thefirst AP that accepts it, UEs located near overlapping beam boundariesmay register with a sub-optimal AP in spite of the fact that the APs areoperating on different channels.

A UE located along a single azimuth direction (e.g. 88° in FIG. 8) mayregister according to one of three possible outcomes by communicatingwith APs at one of three possible beam locations 810, 811 or 812. In thefirst outcome, the UE registers with an optimal AP associated with beam1L 802 at beam location 810. In the second outcome, the UE registerswith a sub-optimal AP associated with beam 1R 803 at beam location 811.In the third outcome, the UE registers with one of two sub-optimal APsassociated with a sidelobe 807 of beam 2L 801 or beam 2R 804 at beamlocation 815. To identify the actual outcome, all APs may report to acontroller (e.g., controller 408 of FIG. 4) the signal level from eachUE communicating therewith, for example, together with a UE identifiersuch as a basic service set identifier (BSSID) (e.g. the media accesscontrol (MAC) address of the wireless access point (WAP) for each UE).If the UE has registered to a sub-optimal AP on an overlapping beam(e.g. at location 811) or on a sidelobe (e.g. at location 815), anotheroptimal AP will report a stronger received signal (e.g. at location 810)than the level reported by the registered AP. The sub-optimal APsassociated with overlapping beam 803 or with sidelobe 807 may reject theregistration of the UE at beam location 811 or 815. In one embodiment,the rejected UE may subsequently be instructed to register with theoptimal AP associated with beam 802 at beam location 810 (e.g. inaccordance with IEEE 802.11k) or may be allowed to continue scanning thechannels and register again, iteratively repeating the registrationprocess, until it finds and registers with the optimal AP associatedwith beam 1L 802. The latter embodiment may be examined by comparingbeam locations 810 and 811. Since beam location 810 shows a situation inwhich a UE registers to an AP over the primary lobe of beam 1L 802providing a greater than threshold relative signal strength relative tothe signal strength received over other beams 2R 804 of other APs on thesame channel, the registration of the UE to the AP beam 1L 802 may bemaintained. For example, when the UE is registered at beam location 810of beam 1L 802, the AP associated with beam 1L 802 experiences arelatively higher gain/amplitude (and therefore a higher received signallevel) of approximately 11 dB than the received signal by the sidelobeof co-channel beam 2R 804 as indicated by dashed line 813. However, beamlocation 811 shows a less desirable situation in which a UE registers toan AP over the primary lobe of adjacent beam 1R 803 providing a lessthan threshold relative signal strength relative to signals receivedover beam 2L 801 of the other co-channel AP. For example, when the UE isregistered at beam location 811 of beam 1R 803, the AP associated withbeam 1R 803 experiences approximately 6 dB lower gain or SNR indicatedby dashed line 814 when its co-channel AP is operating on beam 2L 801.Accordingly, the registration of the UE to the AP associated withadjacent beam 1R 803 may be rejected.

In one embodiment, rejecting the registration of the UE to a sub-optimalAP may improve signal quality for the UE. In this example the UE may beroaming or located close to a boundary between beams. In conventionalsystems, as the UE moves closer and closer to the boundary and thesignal worsens and worsens, the AP connection is maintained until theconnection is so bad that it no longer meets the UE's registrationstandards. In contrast, according to embodiments of the invention, theAP may end or reject the registration when another non-registered APprovides a relatively higher signal strength than the currentlyregistered AP, for example, before the signal quality degrades to levelsbelow registration standards. Accordingly, the signal strength of thecommunication between the UE and the registered AP may be reassigned toa better AP in spite of being above the minimum signal strength allowedby the UE's registration standards for being rejected, thereby improvingsystem communication.

According to an embodiment of the invention, a system and method ofcommunicating in a wireless multi-beam network is provided foroptimizing signal reception quality in a communication channel betweenan AP and a UE. Embodiments of the invention may enable the UE toselectively register with an AP when the ratio of the power level ofsaid channel beam to the power level of another (suboptimal) channel orbeam, such as a sidelobe of a co-channel beam, satisfies a predefinedthreshold. A plurality of APs may receive, measure and report to acontroller, their respective power levels received from the same UE. Thecontroller may determine if the UE ratio of received signal power levelsis within a predefined threshold range. The controller may select anoptimal communication channel for the UE based on said thresholddetermination. The controller may use the predefined threshold of thesignal power ratios to select between the signal presented in a desiredchannel over that of an undesirable channel, as may be present in asidelobe channel. The controller may determine if the predefinedthreshold is further defined to be approximately, for example, 6 dB.Other measurements of signal strength ratios may be used.

According to embodiments of the invention, when a UE registers to asystem and is detected by only one AP, no re-registration takes place.If the UE is detected by two or more APs (e.g. two in the case of a4-beam system), the controller may determine if the UE is registered toan optimal or suboptimal beam/channel/AP based on the relative ratio ofsignal strengths recorded by each AP. If the UE is registered with an APon a stronger signal, for example, where the ratio of signal strength ofthe stronger signal to a weaker signal with another AP is greater than apredetermined threshold (e.g., >6 dB), the controller may determine thatthe UE is registered with the optimal beam/channel/AP and nore-registration takes place. If the UE is registered with an AP onanother signal, for example, where the ratio of signal strength of thestronger signal to a weaker signal with another AP is less than apredetermined threshold (e.g., <6 dB), the controller may determine thatthe UE is registered with a suboptimal beam/channel/AP and may assignthe UE to re-register with the AP associated with the stronger signal oranother AP. Further, if the UE is registered but the ratio of receivedsignal levels is less than the threshold, the controller may determinethat neither beam/AP is ideal, and that another beam/AP may be ideal,which cannot be detected because the UE is registered on a differentchannel (frequency) than the ideal beam/AP. Accordingly, the AP mayreject the sub-threshold registration and re-register either byrequiring the UE to re-scan channels to repeat the above steps or may bedirectly assigned to a new AP (e.g., when using the IEEE 802.11kprotocol) and verify the assignment is to the optimal AP/beam byrepeating the above steps.

According to some embodiments, in order to support the maximumcapability offered by WiFi, 64-quadrature amplitude modulation (QAM) maybe used. Systems using 64-QAM typically require at least a −20 dB signalto interference (sidelobe) ratio in order to achieve acceptableperformance. As described above, antenna element tapering (e.g., Taylorweighting) may reduce sidelobe interference when the antenna arrays arelarge (e.g., eight antenna elements or more). A disadvantage of taperinghowever is it reduces antenna array efficiency thereby lowering theachievable gain. For this reason, systems typically use tapering, whichmay be insufficient to effectively suppress sidelobe interferences todesired levels. Accordingly, embodiments of the invention may provide acombination of tapering and a signal cancellation technique to reducesidelobe interference.

Reference is made to FIG. 9, which schematically illustrates amulti-beam system 900 for tapering and signal cancellation in accordancewith an embodiment of the invention. FIG. 9 may include one or morebeamforming functions 901 to taper signals to/from a plurality ofantennas 902-905 with weights w₁, w₂, w₃ and w₄ 910-913 totransmit/receive a plurality of tapered beams 906-909, respectively. Inaddition, beamforming function 901 may use coupling coefficients h₁₃,h₃₁, h₂₄ and h₄₂, 914-917 (e.g. complex weighting functions having realand/or imaginary parts) to couple beams 908, 906, 909, and 907,respectively, for signal cancellation. For example, one beam may becoupled to another beam on the same channel, e.g. h₁₃ is used to couplebeam 906 with beam 908 and h₂₄ is used to coupling beam 907 with beam909, for example, to cancel, suppress or reduce the level or strength ofthe undesired signal being received or transmitted in the sidelobedirection.

Reference is made to FIG. 10, which schematically illustrates aradiation pattern transmitted by the antenna array of FIG. 9 with andwithout signal cancellation in accordance with an embodiment of theinvention. FIG. 10 shows the radiation gain versus the azimuth of thesignal without signal suppression (solid lines) and with tapering andsignal cancellation (dashed lines). For clarity, only two co-channelbeams are shown, for example, beam 1L 1001 and beam 2R 1002, although asimilar radiation pattern exists for the beams 1R and 2L on the otherchannel. Lines 1003-1006 identify the subsector boundaries for the twobeams 1001 and 1002.

FIG. 10 shows the level of the sidelobes from one beam in the directionof the other. Trace 1007 identifies the level of beam 2R 1002 in thedirection of beam 1L 1001 and trace 1008 identifies the level of thesidelobes of beam 1L 1001 in the direction of beam 2R 1002, all withoutsignal cancellation. Similarly, trace 1009 identifies the level of beam2R 1002 in the direction of beam 1L 1001 and trace 1010 identifies thelevel of the sidelobes of beam 1L 1001 in the direction of beam 2R 1002,all with signal cancellation. Line 1011 shows the threshold levelrequired for a worst case of sidelobe interference of e.g. −20 dB fromthe lowest beam gain within the subsector. Shaded areas 1012-1017 definedirections that do not meet that criterion.

Reference is made to FIG. 11, which schematically illustrates aradiation pattern transmitted by the antenna array of FIG. 9 withtapering and selective signal cancellation in accordance with anembodiment of the invention. The radiation plots of FIG. 11 show thegains or amplitudes of the same co-channel beams 1L 1101 and 2R 1102after tapering of the elements has been applied. In the example shown inFIG. 11, tapering weights W1-W4 (e.g. 910-913 of FIG. 9) are 0.7, 1.0,1.0 and 0.7, respectively. A comparison of the radiation patterns FIG.10 (without tapering) and FIG. 11 (with tapering) shows that aftertapering the primary lobe beam to sidelobe ratio is approximately 16 dBin FIG. 11 compared to the non-tapered ratio of approximately 13 dB inFIG. 10, which has little or no tapering, and at the subsectorboundaries, after tapering the ratio is approximately 13 dB in FIG. 11compared to the non-tapered ratio of approximately 9 dB in FIG. 10.Traces 1110 and 1111 correspond to the signal cancellation achieved by abeamformer applying coupling coefficients h₂₄ and h₄₂ (e.g. 916 and 917of FIG. 9) to beams 2R and IL (e.g. 909 and 907 of FIG. 9),respectively. Traces 1110 and 1111 show that, although the combinationof tapering and signal cancellation may increase the primary lobe tosidelobe ratio, the ratio is still less than the 20 dB threshold used tosupport 64-QAM. Accordingly, additional measures may be used to achievethe 20 dB threshold ratio. One such measure is selective signalcancellation.

FIG. 10 shows that in the direction of beam 1L 1001, signal cancellationor coupling may reduce the strength of sidelobe signals of co-channelbeam 2R from 1007 to 1009 near the boundaries 1003 and 1004 of the 1Lsubsector. However, near the center of the subsector (e.g. an azimuthrange of approximately)75-85°, signal cancellation or coupling adds aninterference artifact 1013 for beam 1L 1001 and 1016 for beam 2R 1002 inFIGS. 10 and 1110 and 1111 in FIG. 11. Thus, signal cancellation mayimprove the primary lobe to sidelobe ratio near subsector boundaries (inthe sidelobe directions), but may worsen the ratio near the subsectorcenter (in the primary lobe direction) where there are typically nosignificant sidelobes. The benefit of signal cancellation may thereforedepend on the location of a UE in the subsector. Accordingly,embodiments of the invention may selectively activate signalcancellation based on the UE location. When the UE is near the subsectorboundaries and sidelobe interference is above a threshold ratio,beamformer may apply signal cancellation. However, when the UE is nearthe subsector center and sidelobe interference is below a thresholdratio, beamformer may not apply signal cancellation. To determine thelevel of sidelobe interference and thus the location of the UE,embodiments of the invention may conduct a signal cancellation test,turning signal cancellation on and then off, to determine whether or notinterference is reduced or increased by the signal cancellation. Ifinterference is reduced, signal cancellation may be turned on forcontinued communication with the UE, while if interference is increased,signal cancellation may be turned off.

Reference is made to FIG. 12, which schematically illustrates amulti-beam system 1200 for selective signal cancellation using digitalbeamforming in accordance with an embodiment of the invention. A UEsignal may be received by two or more APs, for example, over beam 1L1101 and beam 2R 1102 of FIG. 11, where one is received on a sidelobe.In one example configuration, the signal received over beam 1L 1101 isstronger than that received over beam 2R 1102, although a correspondingtechnique applies if the beam 2R 1102 signal is stronger than that thebeam 1L 1101 signal. System 1200 may provide a test to determine ifsignal cancellation is effective or not. In one step, signalcancellation may be turned off and the beamformer may not activate acoupling coefficient h₂₄ 916 of FIG. 9. When signal cancellation is off,a radiation pattern may reveal the sidelobe patterns 1112 and 1113 ofbeam 2R 1102 shown in FIG. 11 in which a UE is not in the direction ofthe center of the beam 1L 1101 (e.g. an azimuth range of)75-85° but in alocation either to the right of the beam center at 1113 (e.g. an azimuthrange of)60-75° or to the left of the beam center at sidelobe 1112 (e.g.an azimuth range of)85-90° because the sidelobe level in the directionof the center of beam 1L 1101 is nearly null (zero). In another step,coupling may be turned on and the beamformer may activate the couplingcoefficient h₂₄ 916 of FIG. 9. When signal cancellation is on, aradiation pattern may reveal a UE located in the direction of the centerof beam 1L 1101 because the signal cancellation pattern of trace 1110 ofFIG. 11 shows that the sidelobe level of beam 2R 1102 is high in thedirection of the center of beam 1L 1101 and not off center.

According to one embodiment of the invention, each AP may use the twoon/off signal cancellation modes to test whether or not to activatesignal cancellation by measuring and recording the better performingmode (e.g. whether interference was lower with coupling coefficient h₂₄916 on or off). Each AP may identify which signals are from each UE bythe signal's UE identification code (e.g., MAC address). Subsequentlyafter an AP (e.g. AP #2 1209 assigned to beam 1L of FIG. 12) receivessignals from a UE in both on and off modes and identifies the preferredmode, the AP informs the controller (e.g. controller 1203 of FIG. 12) ofthe preferred mode (e.g. turn coupling coefficient h₂₄ 916 of FIG. 9 onor off) that produces the best performance when receiving UE signals(e.g. with beam 2R 1102 of FIG. 11). If neither mode with couplingcoefficient h₂₄ 916 on or off reduces the UE signal received by twobeams/APs, the UE may be too close to the antenna array(s). In suchcases, the UE may be assigned to communicate with an alternateAP/channel using an antenna that covers the whole sector.

In another embodiment, once the aforementioned UE has been identified,the controller 1203 may command the logical block element 1207 toperform real time cancellation or suppression of the specific UE signalcomponent received in beam 2R 1102 from that UE based on filtering andcancelling using finite impulse response (FIR) and correlationtechniques, and the stronger signal received in beam 1L 1101.

Embodiments of the invention may reduce interference from the sidelobesof beam 2R 1102 for UEs located in the direction of beam 1L 1101, whichmay reduce the UE signal strength received at the AP #4 1210 assigned tobeam 2R 1102. Such embodiments may similarly apply to the alternate beamby substituting h₄₂ 917 for h₂₄ 916, beam 2R 1102 for 1L 1101 and beam1L 1101 for beam 2R 1102 to reduce interference from the sidelobes ofbeam 1L 1101 for UEs located in the direction of beam 2R 1102, which mayreduce the UE signal strength received at the AP #2 1209 assigned tobeam 1L 1101.

According to an embodiment of the invention, a system and method isprovided for using a controller to select an optimal channel and/or beamin a wireless network. Entry of a UE may be detected in a sector thatcontains a plurality of beams for communicating with a plurality ofaccess points. A sub-optimal UE registration may be determined within anAP's beam subsector. A more optimal reception channel may be selectedusing a predefined algorithm directed to the slope of a selected beam.An optimal communication channel may be selected by comparing theoffered signal quality available to a UE by using said controller toassess the effect of selectively applying signal cancellation methodsto/at the access points. An optimal communication channel may beselected when in the presence of both a desired beam and a sidelobebeam. The impact of applying signal cancellation methods may bedetermined by selectively activating and deactivating beam to beamsignal coupling or signal cancellation using coupling coefficients, forexample, h₁₃, h₃₁, h₂₄ and h₄₂.

Traces 1110 and 1111 of FIG. 11 show that when applying signalcancellation according to embodiments of the invention, the sideloberatio is rarely worse than −20 dB and has a worse case of −17 dB foronly a small percentage of directions. According to an alternativeembodiment of the invention, signal cancellation may be appliedcontinuously to sufficiently reduce the sidelobe ratio to belowthreshold (e.g. −20 dB) in most cases, leaving a small percentage ofcases in which the sidelobe ratio is above threshold. However, this −20dB threshold may be required for only some types of modulation (e.g.64-QAM). Accordingly, in one embodiment, some UEs located in belowthreshold directions may communicate with less efficient modulation. Inanother embodiment, APs may detect and record the modulation used byeach UE, and may apply selective signal cancellation for modulationsrequiring a relatively higher range of the sidelobe rejection ratios(e.g. 64-QAM requiring greater than a 20 dB ratio) and apply continuoussignal cancellation for modulations requiring a lower range of thesidelobe ratios (e.g. 16-QAM requiring greater than approximately a 14dB ratio).

According to an embodiment of the invention, a system and method isprovided for operating a controller in a wireless network. Embodimentsof the invention may include detecting the entry of a UE in a sectorcontaining a plurality of beam spaces offered by a plurality of accesspoints. Signal cancellation may be continuously, indiscriminately ornon-selectively applied to all signals, for example, upon detecting areceived signal cancellation indicator from said controller identifyingthe presence of a sidelobe channel. Embodiments of the invention mayinclude allocating any UE with a less that optimal signal power to analternate access point. Embodiments of the invention may includedetecting the modulation of each UE and may apply selective signalcancellation only to UEs operating in 64 QAM mode and continuous signalcancellation to UEs operating in all other modulations, for example,allowing higher sidelobe interference.

The signal strength information gathered and recorded from each UEduring reception periods by an AP may be used to reduce interferenceduring transmission periods. Referring to FIGS. 11 and 12, when AP #41210 associated with beam 2R 1102 transmits signals, the signalradiation from sidelobes 1112 and 1113 may cause interference withtransmissions by AP #2 1209 to UEs in the subsector covered by beam 1L1101. When an AP is transmitting on beam 2R with AP #4, and AP #2 isattempting to communicate to a UE in its subsector using beam 1L, thesystem may use the information previously measured and recorded thatestimated the advantage or disadvantage of coupling for the UE toinstruct the logical block element whether or not to apply signalsuppression or cancelling. For example, if during a reception period, anAP determines that when receiving signals from the UE on beam 1L signalcancellation using coupling coefficients h₂₄ 916 substantiallysuppressed reception on that beam by AP #4, the coupling signal h₄₂ 917may be used for the transmission to prevent transmissions of beam 2Rfrom interfering with transmissions to that UE on beam 1L. As the systemprepares to send data to a specific UE, the controller checks its storedprofile on that specific UE, determining various parameters for that UEincluding the negotiated data rate. As part of that decision logic, thesystem controller may determine if applying signal cancellation isappropriate and, if so, instructs the logical block element of theupcoming transmission and duration of the transmission, for example, asindicated in a network allocation vector (NAV) counter. The systemcontroller may then create a datagram or other communication unit tosend to the UE as soon as other conditions such as clear channelassessment (CCA) are satisfied. The system controller may create signalcancellation information in advance of actually transmitting thedatagram. The optimal time for the logical block element to implementsignal cancellation, or not, may be coincident with or simultaneous tothe transmission of the signal. This optimum time may be achieved by theAP generating a timing strobe coincident with the data transmission. Thelogical block element may initiate signal cancellation, or not,coincident with this timing strobe, for example, for the duration of theNAV value. A near optimal timing by the logical block element may occurif the logical block element cancels or does not cancel the signalwithin several microseconds (μ sec) of the actual transmission by theUE. There is typically no significant degradation of the signal if thesignal cancellation is early. If the signal cancellation is late, asignal preamble may experience a reducedsignal-to-interference-plus-noise ratio (SINR). However, since thepreamble is typically sent at a much lower modulation rate, the impactmay be negligible. Further, data frames transmitted/received in thesignals may include forward error correction (FEC) bits, which may beused to correct any errors caused by delayed signal cancellation toprevent retransmission.

According to an embodiment of the invention, a system and method isprovided for optimizing reception quality in a wireless network betweenan access point and a user equipment apparatus. Embodiments of theinvention may include detecting entry of a user equipment in a sectorcovered by a plurality of beams provided by a plurality of accesspoints, measuring and determining the effect of applying signalcancellation methods for said user equipment, reporting to thecontroller the specific identifiers of said user equipment prior totransmission, allowing the controller to select an optimal signalcancellation function or coupling coefficients hij to apply duringreceive intervals as a function of the received signal over each beam ito the received signal over each beam j, and applying signalcancellation during transmit intervals as an inverse or transpose ofcoupling coefficients hji when transmitting over both beams i and j. Thecoupling coefficients h_(ji) for signal cancellation may be appliedcoincident with the transmission over beams and j. Embodiments of theinvention may include continually applying said method to all userequipment. Embodiments of the invention may include allocating any userequipment with less that optimal signal power to an alternate accesspoints. Embodiments of the invention may include detecting a userequipment operating in 64 QAM mode, applying selective signalcancellation methods only to those user equipment operating in 64 QAMmode.

Reference is made to FIG. 13, which schematically illustrates amulti-beam system 1300 for selective signal cancellation using digitalbeamforming in accordance with an embodiment of the invention. System1300 may include separate receive and transmit antenna arrays 1301 and1302 as described in reference to FIG. 4. System 1300 may include aplurality of radios 1308 to process RF signals at antenna arrays 1301and 1302. Radios 1308 may include a plurality of upconverters (UC) A, Band C and downconverters (DC) A, B and C to support a plurality of (e.g.N=3) channels. “UC A” and “DC A” may provide communication over onechannel A assigned to two or more access points (e.g., AP #1 and AP #3).“UC B” and “DC B” may provide communication over another channel Bassigned to two or more other access points (e.g., AP #2 and AP #4). Theplurality of APs (e.g. AP #1-AP #4) may generate a multi-beam systemsubdividing an area of coverage (e.g. area 225 of FIG. 2) into aplurality of subsector zones or beams over which the APs mayindependently communicate with UEs. Adjacent beams may operate overalternating channels A and B to minimize interference at zonesboundaries, as described in reference to FIG. 7. According to anembodiment of the invention, an additional access point (e.g., AP #5)may provide a sector beam spanning across the entire area (or at leastacross multiple subsector zones). The additional access point mayoperate on an independent channel C different from channels A and B, forexample, to avoid interference with overlapping beams associated withother APs 1-4. In the example shown in FIG. 13, a logical block elementsuch as the FPGA 1307 may connect the signals from all antenna elementsin arrays 1301 and 1302 with UC C and DC C to form the sector beam. Inanother embodiment, only one of the antenna elements (e.g. an outer-mostelement) may be used to form the sector beam, which may be operated atreduced power case because of tapering for the other channels A and B.

Reference is made to FIG. 14, which is a flowchart of a method inaccordance with an embodiment of the invention. Operations described inreference to FIG. 14 may be executed using one or more processor(s)disposed in devices shown in FIGS. 7, 9, 12 and/or 13, such as,controllers 408, 708, 1203 and/or 1303 and/or APs 401, 701, 1209/1210and/or AP#1-5 of FIG. 13.

In operation 1410, a processor may receive an indication that each of aplurality of APs have each received a signal or transmission from thesame user equipment (UE) over the same channel. The UE reception is witheach AP over an associated beam. The UE may communicate with an optimalAP over a primary lobe providing relatively higher signal strength orsuboptimal APs over one or more surrounding sidelobes providingrelatively lower signal strength. The AP may identify a signal from theUE by receiving an associated UE identifier such as a BSSID in thesignal.

In operation 1420, a processor may determine that the first one of theplurality of APs to satisfy registration requirements associated withthe UE may register the UE. The first registered AP may be an optimal orsuboptimal AP.

In operation 1430, each AP may report to the processor informationrelated to the signal strength of communication received at the AP fromthe UE. Depending on the relative signal strengths received at each AP,a process or processor may proceed to operation 1440 or 1450.

In operation 1440, if the controller determines that the signal strengthreceived at the registered AP is greater than the signal strengthreceived at one or more of the non-registered APs by more than athreshold amount, the processor may maintain the registration betweenthe UE and AP in operation 1420. The registered AP may receive such anabove threshold relative signal strength when the UE communicates withthe registered AP over a primary lobe.

In operation 1450, if the controller determines that the signal strengthreceived at the registered AP is not greater than (e.g. less than orequal to) the signal strength received at one or more of thenon-registered APs by a threshold amount, the processor may reject theregistration between the UE and AP in operation 1420. The non-registeredAP may receive such a signal strength when the UE communicates with thenon-registered AP over a primary lobe and the registered AP over asidelobe.

A process or processor may proceed to operation 1460 if the UE iscapable of being directed to a specific AP, for example, operatingaccording to the IEEE 802.11k protocol. For such a UE, a processor maydirect the UE to re-register or associate with a non-registered AP thatreceives signals from the UE having a signal strength that is greaterthan the signal strength received at the registered APs by more than athreshold amount. Accordingly, the condition of operation 1440 issatisfied and the process or processor ends. Otherwise, process orprocessor may proceed to operation 1470.

In operation 1470, a processor may direct the AP to reject registrationof the UE to the registered AP by either denying the UE ability toregister (e.g. authenticate) or by sending the UE a de-authenticationmessage.

In operation 1480, the UE may re-scan the channels, repeating the aboveoperations 1410-1430 to iteratively re-register with a new AP until theUE re-registers with an AP receiving an above threshold relative signalstrength at operation 1440 and the process or processor ends.

Reference is made to FIG. 15, which is a flowchart of a method inaccordance with an embodiment of the invention. Operations described inreference to FIG. 15 may be executed using one or more processor(s)disposed in devices shown in FIGS. 7, 9, 12 and/or 13, such as,controllers 408, 708, 1203 and/or 1303 and/or APs 401, 701, 1209/1210and/or AP#1-5 of FIG. 13.

In operation 1510, a processor may receive an indication that a signalis received from a single user equipment (UE) at each of two or more APsover the same channel. A relatively stronger power signal may bereceived over a primary lobe of a communication beam of one of the APsand a relatively weaker power signal may be received over a sidelobe ofa communication beam of another one of the APs.

In some embodiments, a processor may detect the signal modulation of theUE's signal. In operation 1520, the processor may apply continuoussignal cancellation if the modulation allows a below thresholdinterference level (e.g. 16-QAM requires greater than approximately a 14dB SNR, but less than a threshold of 20 dB SNR). In operation 1530, theprocessor may apply the selective signal cancellation of operations1550-1560 or 1570 if the modulation requires an above threshold maximuminterference level (e.g. 64-QAM requires greater than the threshold of20 dB SNR). Operations in 1520-1540 may be optional. In otherembodiments, selective signal cancellation is automatically used and nomodulation is detected.

In operation 1550, a processor may test the efficacy of signalcancellation by turning signal cancellation on and off to measure the UEsignals at the registered AP or other APs.

In operation 1560, if interference at the AP is lower when signalcancellation is turned on, a processor may apply said signalcancellation for continued communication with said UE. The processor mayapply signal cancellation to suppress sidelobe signals if the UE isdetermined to communicate over a sidelobe, but not applying signalcancellation if the UE is determined to communicate over a primary lobe.The processor may apply said signal cancellation by modulating thesignals by coupling coefficients h_(ij) of each beam i signal to eachbeam j signal.

In operation 1570, if interference is lower when signal cancellation isturned off, a processor may communicate with said UE without applyingsaid signal cancellation.

In some embodiments, in optional operation 1580, if a greater thanthreshold amount of interference is experienced when signal cancellationis both on and off, a processor may control an additional AP to providean additional channel of coverage, for example, using an antenna thatcovers an entire sector serviced by the two or more APs.

Other operations or orders of operations may be used.

According to an embodiment of the invention, a system and method isprovided for operating a wireless network. Embodiments of the inventionmay provide additional sector coverage by allocating an additionalaccess point upon detecting conditions indicating a use for additionalcoverage.

As will be appreciated by one skilled in the art, signal or sidelobesuppression, cancellation or reduction may refer to reducinginterference e.g. due to sidelobe or other noise, to a below thresholdamount or ratio such as SINR or a ratio of sidelobe gain to primary lobegain. The threshold may be specified according to a communicationstandard, modulation standard, or other device or network requirement,and may allow some interference e.g. below a threshold level. Forexample, signal cancellation of a signal may only reduce, suppress, orpartially cancel interference, noise or sidelobe artifacts.

As will be appreciated by one skilled in the art “selective signalcancellation” may refer to activating or deactivating signalcancellation based on a condition related to the efficacy of the signalcancellation, e.g., if signal cancellation reduces signal interferenceor reduces said interference by an amount greater than when no signalcancellation is used. In contrast, “continuous signal cancellation” mayrefer to activating signal cancellation without testing or predictingthe efficacy of the signal cancellation. Continuous signal cancellationmay be activated, for example, based on a condition unrelated tointerference, such as, the signal modulation or device, network orcommunication standards.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or an apparatus. As such,any limitations commonly associated with the term “FPGA” should not beconstrued to be implementation technology specific; rather it may beembodied in any logical apparatus. Accordingly, aspects of the presentinvention may take the form of an entirely hardware embodiment, anentirely software embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system.”

In some embodiments, access points (e.g., APs 401, 701, 1209/1210 and/orAP#1-5 of FIG. 13) may passively transfer signal information from UE toa controller (e.g. controller 408, 708, 1203 and/or 1303), whichcompares relative signal strengths between APs to thresholds, makesdecisions regarding relative signal strength, determines whether tomaintain or reject registration between UEs and APs for selectiveregistration, and determines whether to apply signal cancellation. Inanother embodiment, such operations may be executed by another device inFIGS. 7, 9, 12 and/or 13, for example, access points (e.g., APs 401,701, 1209/1210 and/or AP#1-5 of FIG. 13). In various embodiments, theprocessor(s) executing the operations of FIGS. 14 and 15 may be located,in part or in whole, in one or more controllers such as a base stationcontroller (BSC) or other centralized network device, or in one or moreAPs or base stations (BSs).

The aforementioned block diagrams illustrate the architecture,functionality, and operation of possible implementations of systems andmethods according to various embodiments of the present invention. Inthis regard, each block in the flowchart or block diagrams may representa module, segment, or portion of code, which comprises one or moreexecutable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In the above description, an embodiment is an example or implementationof the inventions. The various appearances of “one embodiment,” “anembodiment” or “some embodiments” do not necessarily all refer to thesame embodiments.

Although various features of the invention may be described in thecontext of a single embodiment, the features may also be providedseparately or in any suitable combination. Conversely, although theinvention may be described herein in the context of separate embodimentsfor clarity, the invention may also be implemented in a singleembodiment.

Reference in the specification to “some embodiments”, “an embodiment”,“one embodiment” or “other embodiments” means that a particular feature,structure, or characteristic described in connection with theembodiments is included in at least some embodiments, but notnecessarily all embodiments, of the inventions.

It is to be understood that the phraseology and terminology employedherein is not to be construed as limiting and are for descriptivepurpose only.

The principles and uses of the teachings of the present invention may bebetter understood with reference to the accompanying description,figures and examples.

It is to be understood that the details set forth herein do not construea limitation to an application of the invention.

Furthermore, it is to be understood that the invention can be carriedout or practiced in various ways and that the invention can beimplemented in embodiments other than the ones outlined in thedescription above.

It is to be understood that the terms “including”, “comprising”,“consisting” and grammatical variants thereof do not preclude theaddition of one or more components, features, steps, or integers orgroups thereof and that the terms are to be construed as specifyingcomponents, features, steps or integers.

If the specification or claims refer to “an additional” element, thatdoes not preclude there being more than one of the additional element.

It is to be understood that where the claims or specification refer to“a” or “an” element, such reference is not be construed that there isonly one of that element.

It is to be understood that where the specification states that acomponent, feature, structure, or characteristic “may”, “might”, “can”or “could” be included, that particular component, feature, structure,or characteristic is not required to be included.

Where applicable, although state diagrams, flow diagrams or both may beused to describe embodiments, the invention is not limited to thosediagrams or to the corresponding descriptions. For example, flow neednot move through each illustrated box or state, or in exactly the sameorder as illustrated and described.

Methods of the present invention may be implemented by performing orcompleting manually, automatically, or a combination thereof, selectedsteps or tasks.

The term “method” may refer to manners, means, techniques and proceduresfor accomplishing a given task including, but not limited to, thosemanners, means, techniques and procedures either known to, or readilydeveloped from known manners, means, techniques and procedures bypractitioners of the art to which the invention belongs.

The descriptions, examples, methods and materials presented in theclaims and the specification are not to be construed as limiting butrather as illustrative only.

Meanings of technical and scientific terms used herein are to becommonly understood as by one of ordinary skill in the art to which theinvention belongs, unless otherwise defined.

The present invention may be implemented in the testing or practice withmethods and materials equivalent or similar to those described herein.

While the invention has been described with respect to a limited numberof embodiments, these should not be construed as limitations on thescope of the invention, but rather as exemplifications of some of thepreferred embodiments. Other possible variations, modifications, andapplications are also within the scope of the invention. Accordingly,the scope of the invention should not be limited by what has thus farbeen described, but by the appended claims and their legal equivalents.

The invention claimed is:
 1. A method for selective registration of auser equipment (UE) to one of a plurality of access points (APs) in amulti-beam system, the method comprising: receiving an indication thateach of a plurality of APs have received a signal from a single UE,wherein the UE communicates with each AP over an associated beam thatincludes a primary lobe providing a relatively higher signal strengthsurrounded by one or more sidelobes providing a relatively lower signalstrength; registering the UE to a first one of the plurality of APs thatsatisfies registration requirements associated with the UE; andmaintaining the registration of the UE to the registered AP if the UEcommunicates with the registered AP over a primary lobe providing agreater than threshold relative signal strength relative to the otherAPs, or rejecting the registration of the UE to the registered AP if theUE communicates with the registered AP over a sidelobe or over a primarylobe providing a less than threshold relative signal strength relativeto the other APs.
 2. The method of claim 1 comprising receiving a reportfrom each of the plurality of APs including information related to thesignal strength of communication between each AP and the UE and a UEidentifier uniquely identifying the UE.
 3. The method of claim 1,wherein the relative signal strength for each AP is a ratio of theamplitude of signals communicated between the UE and the AP over theamplitude of signals communicated between the UE and another AP.
 4. Themethod of claim 1, wherein the relative signal strength for each AP is asignal-to-noise ratio (SNR) or a signal-to-interference-plus-noise ratio(SINR).
 5. The method of claim 1 comprising, if the registration isrejected, registering the UE to the AP having the highest relativesignal strength.
 6. The method of claim 1 comprising, if theregistration is rejected, said selective registration method of claim 1is iteratively repeated until the UE provides a greater than thresholdrelative signal strength.
 7. The method of claim 1, wherein theregistration is rejected before the signal quality degrades to levelsbelow registration standards.
 8. A system for selective registration ofa user equipment (UE) to one of a plurality of access points (APs) in amulti-beam system, the system comprising: a processor adapted to:receive an indication that each of a plurality of APs have received asignal from a single UE, wherein the UE communicates with each AP overan associated beam that includes a primary lobe providing a relativelyhigher signal strength surrounded by one or more sidelobes providing arelatively lower signal strength, register the UE to a first one of theplurality of APs that satisfies registration requirements associatedwith the UE, and maintain the registration of the UE to the registeredAP if the UE communicates with the registered AP over a primary lobeproviding a greater than threshold relative signal strength relative tothe other APs, or reject the registration of the UE to the registered APif the UE communicates with the registered AP over a sidelobe or over aprimary lobe providing a less than threshold relative signal strengthrelative to the other APs.
 9. The system of claim 8, wherein theprocessor is adapted to receive a report from each of the plurality ofAPs including information related to the signal strength ofcommunication between the AP and the UE and a UE identifier uniquelyidentifying the UE.
 10. The system of claim 8, wherein the relativesignal strength for each AP is a ratio of the amplitude of signalscommunicated between the UE and the AP over the amplitude of signalscommunicated between the UE and another AP.
 11. The system of claim 8,wherein the relative signal strength for each AP is a signal-to-noiseratio (SNR) or a signal-to-interference-plus-noise ratio (SINR).
 12. Thesystem of claim 8, wherein if the registration is rejected, theprocessor is adapted to register the UE to the AP having the highestrelative signal strength.
 13. The system of claim 8, wherein if theregistration is rejected, the UE is allowed to iteratively repeat saidselective registration until the UE provides a greater than thresholdrelative signal strength.
 14. The system of claim 8, wherein theprocessor is adapted to reject the registration before the signalquality degrades to levels below registration standards.